1. Field of the Invention
The present invention relates to a light emitting device and a lighting device using a semiconductor light emitting element.
2. Description of the Related Art
There has been a line light source and the like employing a light emitting device, which comprises a discharge tube such as a fluorescent lamp or a semiconductor light emitting element, as a lighting device of a document reader in an information processor such as a facsimile, copier, and image scanner. In recent years, downsizing of devices have been carried forward and a line light source using semiconductor light emitting elements has become mainstream. Such line light sources include a direct lighting type in which a plurality of light emitting devices are arranged in line so that light from each of the light emitting devices is projected directly onto a document etc. and a light guide type in which one or more light emitting devices are arranged at an end portion of a transparent light guide having a bar shape or a plate shape so as to introduce light thereto and then the light is projected onto a document etc. from the light guide (for example, see Japanese Laid-open Patent Application Nos. 2003-23525 and 2005-217644).
A conventional lighting device using a light guide is shown in FIG. 4. In a lighting device 500, a light emitting device 400 is arranged at an end surface of a light guide 412 so as to introduce light from the light emitting device to the end surface of the light guide 412. The light guide 412 is set to a white light guide casing 411 such that the emitting surface of the light guide 412 is exposed. Incident light to the light guide 412 is transmitted through the light guide 412 in the longitudinal direction while reflected by the inner surfaces thereof. Then, light is emitted from the emitting surface of the light guide 412 provided along the longitudinal direction so that light can be projected to a document etc. As described above, light is projected not as a point light source but as a surface light source, and thus, the lighting device 500 can emit uniform light. While the direct lighting type described above needs to mount the light emitting devices densely in order to reduce nonuniform emission, the light guide type using a light guide has an advantage in which nonuniform emission can be reduced even with fewer light sources (light emitting devices). Moreover, because the lighting device using a light guide has a simple structure in which a light emitting device is arranged only at the end surface of the light guide, it has an advantage that a complex circuit is not needed and the lighting device can be made thin.
In the light emitting device used in the lighting device described above, as shown in FIG. 3, an opening portion 300A for mounting a light emitting device is provided in a resin package 301 which is provided with a plurality of lead frames 310. The lead frames 310 protrude from a side surface of the package 301 as external connecting terminals. Then, the lead frames 310 are engaged with the circuit substrate of the lighting device and electrically connected thereto so that light can be emitted. The through holes 300D are used for fixing the light emitting device to the light guide casing when assembling a line lighting device.
In the information processors, while downsizing, various performance thereof have been improved year after year, and further improvements in performance have been required. For example, improvements in characteristics such as multifunctionality and operationality enable various processings and also allow users to make effective use, so that the range of usage has been expanding. Also, enhancement of processing capability, that is, capability of high-speed processing is one of the important characteristics. For high-speed processing, high-speed reading of images is necessary. There are several effective ways to achieve this, and among them, increasing the brightness of light illuminating the reading surface of a document is effective, and processing time can be reduced by increasing the quantity of light for reading data.
The amount of light can be increased by increasing the number of light emitting devices that are used as the light source. That is, in the above-described direct lighting type in which a plurality of light emitting devices are arranged in line, it can be achieved by densely mounting the light emitting devices. However, in this case, the size of the lighting device becomes larger so that the image reading device inevitably becomes larger. Moreover, there are negative effects in which the densely mounted light emitting devices produce a large amount of heat, the power consumption is also increased, and deterioration of various electronic components is accelerated, and therefore, it is undesirable to densely mount the light emitting devices.
In the light guide type in which the light emitting devices are mounted at an end surface of the light guide, the area of the end surface is limited. In this case, high power output can be realized by increasing the number of the light emitting elements incorporated in a light emitting device. However, this case is similar to the case described above in that a plurality of light emitting elements, which generate heat, are used. Therefore, problems caused by the generated heat from the light emitting elements occur.
To solve the problems caused by heat generation, in aforementioned Japanese Laid-open Patent Application No. 2003-23525, a material having high heat conductivity is used for the lead frame and thereby improving heat dissipation. In Japanese Laid-open Patent Application No. 2005-217644, heat dissipation is improved by providing an extended portion to the lead frame.
However, even if a material having high heat conductivity is used as described above, a portion of lead frame which is used as a pathway for heat dissipation is narrowed, so that it is difficult to dissipate heat. Therefore, sufficient heat dissipation cannot be obtained.
Also, mounting the light emitting device to the lighting device may be difficult because a plurality of lead frames protrude from the light emitting device. That is, in mounting, the lead frames are inserted in corresponding holes provided in the circuit and the like. Thus, workability may deteriorate when the number of the lead frames increases. In another case, the light emitting device inclines and that may cause deviation of the distance and degree between the light emitting device and the end surface of the light guide from desirable values. If this occurs, output from the light guide decreases. In addition, a part of the exposed lead frame may be bent during the manufacturing process etc., which makes inserting the lead frame into the corresponding hole more difficult.
Accordingly, the present invention is devised to provide a light emitting device capable of effectively dissipating heat generated by high power operation and has superior workability in mounting and less positional displacement.